This invention relates to apparatus for monitoring respiratory performance comprising a pneumatic to electric transducer which is adapted to actuate an electronic read out unit, the transducer including a rotor which comprises vanes which are carried by a rotor spindle for rotation with the spindle about the axis of the spindle and an electric output signal generator which is coupled non-mechanically with the rotor in a manner which results in the read out being a function of rotation of the spindle. Such apparatus will be referred to hereinafter as "Apparatus of the kind described".
Various forms of non-mechanical coupling have been proposed and of these an optical coupling arrangement incorporating photo electric devices has been preferred so far. One disadvantage of this optical coupling arrangement is the need to replace light bulbs from time to time. Another disadvantage is that it is difficult to isolate the output signal generator from the respiratory gas flow that drives the rotor. An object of this invention is to provide another form of apparatus of the kind described which can be arranged so that it does not suffer from these disadvantages.